The plants comprised in this class are multicellular; they are
simple or branched filaments, or expansions consisting of 1 to
several layers of cells; the thallus may be differentiated (as
in many _Florideæ_), to resemble stem, root, and leaf. The cells
contain a distinctly differentiated nucleus (sometimes several),
and distinct chromatophores, coloured by rhodophyll. The chlorophyll
of the chromatophores is generally masked by a red colouring matter
(phycoerythrin), which may be extracted in cold, fresh water; or rarely
by phycocyan. Pyrenoids occur in some. Starch is never formed in the
chromatophores themselves, but a modification--Florideæ starch--may
be found in the colourless protoplasm. Asexual reproduction by motile
or motionless spores (tetraspores) which are devoid of cilia and of
cell-wall. Swarmspores are never found.
Sexual reproduction is wanting, or takes place by the coalescence of
a spermatium and a more or less developed female cell. The spermatia
are naked masses of protoplasm, devoid of cilia and chromatophores.
The female cell (carpogonium) is enclosed by a cell-wall, and after
fertilisation forms a number of spores, either with or without
cell-walls (carpospores), which grow into new individuals.
The Rhodophyceæ may be divided into two families:
1. BANGIOIDEÆ.
2. FLORIDEÆ.